1. Field of the Invention
The present invention relates to an apparatus and a method of producing a fiber web in a dry technique and, more particularly, an apparatus and a method of producing a non-directional (non-oriented) fiber web.
Also, the present invention relates to a fiber web produced from two or more different fiber materials in which the fiber containing ratio of each fiber material to the direction of the thickness of the web is gradually increases or decreases to the direction of the thickness of the fiber web and also, a method of producing the same.
Furthermore, the present invention relates to a fiber web which provides no abrupt change in the physical characteristics to the thickness direction of the fiber web and is thus useful as raw material for a filter, a battery separator, a FRP(fiber reinforced plastics) substrate, an adhesive tape, and so on.
2. Description of the Prior Art
A known apparatus for producing a non-directional fiber web using a dry technique is provided in which fiber material(s) is opened with cylinders equipped with wires, workers, and/or strippers and then, blown by air or sucked.
Also, a prior art apparatus is disclosed (in Japanese Patent Publication No. 31807/1991) in which a fiber material is combed between cylinders which are arranged in a row and rotated in one direction while excessive fibers failing to be transferred to the succeeding cylinder are blown out, and the obtained fiber material is piled.
However, these prior art apparatus are not sufficient for producing a fiber web which is uniform and has no orientation of the web.
It is known that a fiber web is processed to a nonwoven fabric for use as a filter. For increasing the filtering capability and the operational life of a filter, two or more laminated layers of nonwoven fabrics made of fiber materials which are different in fiber diameter are commonly used. Such laminated nonwoven fabrics having two or more layers produce interfaces between layers where pressure loss tends to be increased sharply, and the life of the filter will be shortened. As the physical characteristics are varied abruptly at the interface of the lamination of the nonwoven fabric, the performance of the filter is diminished.
A fiber reinforced plastic (FRP) substrate web is disclosed in Japanese Patent Application Laid-open No. 47740/1991, which comprises monofilaments at one surface side and strands at the other side. Such a substrate web is produced in a manner that when the web is unloaded from the drum, heavy fiber is piled up near the drum and light fiber is piled up far from the drum. This requires that the fiber material contain more than 50% by weight of strands while the rest is made of monofilaments. It is quite difficult to open a given amount of strand to monofilament. Also, a resultant fiber web becomes coarse because of the strand concentrating near the surface.